Agouron Intitute - Microbial oceanography of the oxygen-deficient waters of the eastern tropical South Pacific

Project: Research

Project Details


The eastern tropical South Pacific holds one of the three major oxygen minimum zones (OMZs) of the global ocean. Here, reduced ventilation and the rapid aerobic decomposion of organic matter produced in the productive surface waters create an oxygen-deficient subsurface layer of a few hundred meters thickness. In this oxygen minimum zone, unique microbial processes of global biogeochemical significance occur, in particular anaerobic processes associated with the marine nitrogen cycle, such as denitrification and anammox. Sufficient light can also penetrate the upper part of the OMZ, such that
oxygenic photosynthesis could become a local source of oxygen and reduced carbon. This could allow the co-existence and coupling of aerobic and anaerobic microbial populations and processes.
Furthermore, meso-scale physical activity could also inject oxygen transiently, fueling localized aerobic activity, followed by anaerobic processes once oxygen is consumed. Although it is widely recognized that oxygen should play a key role in the regulation of the microbial processes in the OMZ, our understanding of that regulation has been hampered by the lack of robust methods for measuring very-low oxygen concentrations, and for sampling at the proper space and time scales. Thus, we propose to conduct a microbial oceanographic study of the OMZ of the eastern South Pacific. We wish to determine the main pathways for carbon and nitrogen cycling in the OMZ and to explore how these pathways and their rates are regulated by light and oxygen.
We will use state-of-the-art technology to characterize the spatial and temporal physical and oxygen meso-scale structures within the OMZ, as well as their fine vertical and diel variability. We will
measure dissolved oxygen concentration with newly-developed sensors for nanomolar oxygen concentrations, together with physical and bio-optical properties of the water column with autonomous sea-gliders and yo-yo profilers. For chemical and biological sampling, we will use an advanced CTDPumped-
Profiling System to resolve the upper part of the OMZ (≤200 m) with a high vertical resolution (≤1m) and without oxygen contamination. We will carry out biogeochemical and (global)
gene expression experiments to investigate the effect of low and ultra-low levels of light and oxygen on carbon and nitrogen transformations in controlled incubation systems and along the strong oxygen gradients found in the OMZ.
This will be an international collaborative effort between Chilean, US and Danish researchers and with other ongoing research studies in the region. Our goal is to assemble a multi-disciplinary team of top marine scientists to explore the microbiological and biogechemical functioning of a complex but fascinating marine environment of global significance. This project will build on the previous research conducted within the Agouron-supported project “Dynamics of the oxygen minimum zone (OMZ) in the eastern South Pacific”.
Effective start/end date01/08/200731/12/2023